A sunny Saturday evening, some telephone calls, and a group
of bike-junkie friends ready for a hard-core ride. Maybe this is why we
all like bicycles so much, but when you add three of the best MtB hardtail
frames available this becomes a dream come true. Yes, we had sooo much fun...

It is clear that day by day dual suspensions are gaining market share
and by now there is one that will fit you, but hardtails will always have
that old taste of "this is the way it was before". Their ability
to transfer direct power to the wheel, their amazing acceleration ability,
the finesse needed to ride them (hopping and avoiding to beat your partners
in a downhill), their steering precision. Yes, it is clear that hardtails
will never die.

If you like hardtails or can afford to have more than one MtB there are
some frames available that should be considered as the the base of your
dream bike. We tested three of them that August evening: Cannondale CAAD
5, KHS Alite 4000, and Specialized Stumpjumper M4 .

Aluminum
on the Rocks
It simply happened: Albano Cabria owns a CAAD 5 that he uses to race at
the Cantabrian and Euskadi MtB competitions, provided by his team, the Peñaverán.
Mikel Cadiñanos had just received his new M4 to substitute his former M2.
Mikel broke the right chainstay of that frame, but we will not blame Specialized.
We all know when Mikel tries to sell something he has used, he needs to
hide his name. No buyer would never buy something used a single day by him.
Mikel is what we use to call a bike torturer. The third bike came from Elena
Crespo: Her Alite 4000 is a really nice and light bike, featuring some components
that make the difference between a standard set and a bicycle gourmet dish.

Three aluminum frames, but that is not a coincidence. It would be possible
to build carbon fiber composite frames to be even lighter than the top
alloy ones. A carbon frame could feature interesting damping or shock
absorbing abilities as well as bomb proof lateral stiffness, but it seems
no one but Trek (and Scott out of the hardtail field with their Strike
range) is building them now. Anyways, carbon frames don’t like too much
to interface with stones. They can bear the heaviest extension and compression
loads, but they are quite fragile.

Titanium is a very interesting fame material also. It has good damping
characteristics, natural spring, and almost impossible to wear out if
well worked. But, as aluminum it has a lower density, unless you can achieve
the technology needed to differentially taper and shape titanium tubes
on each of the three dimensions, a top alloy frame will be lighter and
way stiffer than either.

Steel is something that was used in top frames of the past. These days,
the best alloy tubes are tapered and shaped the same way the best steel
tubes are, so there is no way you can build a steel frame to have such
a good stiffness-to-weight ratio as high end aluminum ones do.

Before we tested these frames we needed to know the true weight of each.
Only the KHS could be called "Ultralight" (and by the way that
is the name of its tube set) with 1,400 g (3.086 lbs) in Small- 15"
size. The Specialized reached 1,530 g (3.417 lbs) for a 18" frame,
while the Cannondale marked 1,598 g (3.523 lbs) for its Medium size.

It is clear that manufacturers prefer to sell safe and reliable products
instead of offering stunning marks that could result in failures. Pro
riders are also on this very aware of this even though they could use
a frame for one race and then just throw it away. Two hundred grams will
never mean a victory, but a reliable bike is something essential, so most
of World Cup bikes are a bit over 10 kg (22 lbs).

Burning Neurons
Each of these manufacturers has followed its own way to offer a light and
reliable frame that deserves to be called "top of the range",
but the engineers from any of the three firms earned their salaries when
they developed these babes:

Cannondale
buys customized 6061 tubes from Alcoa. There is not a single tube in the
CAAD 5 that is completely cylindrical. It does not matter if the frame
follows the classic diamond geometry, when you look this bike from less
that 10 meters you can see this frame is very distant from the classic
MtB frame.

Starting from the head tube, the folks at Bedford take an alloy tube
and remove material from the outer central part of its wall at 2/3 of
its circumference. This way it becomes thicker at both extremes to hold
the headset cups, and at its rear side to create a strong area where to
weld the down and top tubes. These tubes do not need any additional reinforcement
welded at its outer side as other top frames do. Cannondale argues that
conventional reinforcements create stress areas and their welds can decrease
the tubes overall endurance. They prefer to create reinforce areas by
softly tapering each tube. This way the stresses are better distributed
throughout all the frame.

This
is why their Power Pyramid Downtube has a thicker wall at the side where
it contacts with the head tube, and why that thickness decreases to the
BB shell, while the outside diameter increases. That BB shell is also
machined to remove aluminum from its central, inner part.

The rear triangle is maybe the most special part of this frame: It is
developed only for disc brakes, so seat stays can be made slimmer and
lighter. They only have to play their structural role in the frame and
do not have to avoid energy losses at the brake system. There are no cantilever
bosses found on the frame. There is neither a need for symmetry now at
this point, so the stays are shaped to allow certain vertical compliance
to make the ride smoother.

The Alite 4000 is a much more classical frame, outwardly at least.
The folks at KHS just take one of the best aluminum tubing available today
and join all its components with flawless welds. But that is not so easy
as it seems: At Rancho Dominguez, CA they have developed a nice geometry
for this frame, it features interesting details such as a snake-shaped
chain and seat stays, a downtube welded gusset, and their unique way of
joining the seat stays.

The frame features a good sloping that makes it easier to steer in hard
conditions without losing stiffness. Other sloping frames are stiff and
light just because they are smaller, but if you measure the weight to
stiffness ratio of the frame plus seat post set, they are not as good
as bikes with higher top tubes with their seat post cut to the correct
length.

The Alite 4000 is as compact as a sloping frame but as stiff as a conventional
one. You will not need to use a super long seat post that would add too
much stress to the top of the seat tube.

And, of course, to weld such a light tubing as the Eatson Ultralight
7005 is not easy. These tubes are extremely thin, so any temperature
excess results in an unrideable frame. For example, the down tube of the
Alite 4000 has a wall thickness of 2.4 mm at the side where it joins the
head tube, while it has just 1.0 mm at its central part and it reaches
1.3 mm at the BB shell side. Interestingly, the transition parts of the
tube (those where the wall thickness increases or decreases) are longer
than those with the thickest wall to avoid stress areas.

The Specialized Stumpjumper M4 is halfway between the KHS and
the Cannondale. It is not as classical as the KHS and not so "aerospatial"
as the Cannondale, but is a class of its own. Its "M4 fully manipulated"
tubing is in fact a custom product from Columbus based on their Starship
series. After a decade where manufacturers proudly declared all the specs
of their tubing, these days they all seem to follow the Trek philosophy:
You don’t need a aerospatial technology lesson, all you need is a rocket.
So, it is impossible to know how they are tapered unless you carefully
cut a frame. We tried to talk "Mikel into cutting his frame, but
he would not agree.

This
is a very nice frame indeed. Pretty paint and cool decals apart, details
arise everywhere: Top tube gusset with an stamped S, downtube box-shaped
reinforcement, no bridge between chainstays (so Mikel will not break this
frame at this point as he did with the M2). The rear triangle is remarkable.
As the chainstays use no bridge between them, they have to be stronger
than usual to keep the frame stiff enough at the BB shell. They are oversized,
ovalized, and shaped the way they don’t interface the chainrings and the
rear wheel due to their large diameter. Add two nice and tiny dropouts,
and a pair of snake seat stays "a-la-Specialized".

What happened to that M2 metal matrix composite used before? Wasn't it
so far ahead from the rest of the aluminum alloys? Yes, it was in the
early nineties when it first came out and was used on Specialized in bikes.
During the first years, the folks at Morgan Hill used a 6061 based composite.
The difference between this composite and a regular 6061 alloy is the
fact that the composite has ceramic oxide particles among the whole alloy
structure. That ceramic particles are not a part of the alloy, and that
is why this matter is called a composite. It is like concrete: Concrete
is just cement with crushed stone, gravel or other dry goods. But not
the cement nor the gravel share at single part of their molecular structure
with the other, so they are not an alloy (it would be impossible since
none of them are metals). They are just a composite, this is, a physical
joint of different materials that create a matter with different characteristics
from the ones of its components. It would be impossible to make a building
not with gravel, nor with cement, but it is possible to make the most
resistant ones using concrete.

In the case of M2 metal matrix composite, the resulting characteristics
are not so far from those from pure 6061 aluminum, because of the very
low percentage of ceramic oxide that is used. Otherwise, the resultant
matter would be not suitable to build bicycle frames. What adds the ceramic
oxide to the aluminum? Hardness and vibration damping abilities, above
all. On the other hand, it is almost impossible to know exactly the mechanical
characteristics of a MMC piece at a given point if not directly observed.
If you are dealing with a large aluminum piece, you know its characteristics
are almost the same throughout all its structure. With MMC you should
apply computerized models to predict the average properties throughout
all the structure, or scan with a tunnel effect microscope the whole structure,
and then determine its exact properties point by point, what is in fact
impossible.

When you use that computerized models to make a Finite Element Analysis
to see how far you can lighten structure (i.e. a frame), it will not allow
you to use the best properties the MMC can achieve, but the average characteristics
the model predicts. So, it is not possible to fight the weight of the
latest ultralight alloys.

Specialized’s latest attempt to save a few more grams without leaving
the MMC path was the use of 7005 alloy as matrix instead of 6061. When
the M4 frames substituted the M2 ones, this meant the good-bye to the
MMC.

It is not Specialized that was wrong when they started to use MMC for
bicycles. During a decade, the M2 frames have been among the best available
What has happened is that bicycle tubing manufacturers have developed
very special alloys to design the lightest and toughest frames that have
surpassed the MMC abilities, and Specialized has recognized it.

The alloy used for the M4 frame is a perfect example of how far the aluminum
technology has gone lately. It contains silicon and magnesium as main
components apart from aluminum, and there are also little percentages
of Cu, Mn and Zn. All this means a 6000 series alloy that is very resistant
to high temperatures the way few millimeters far from the welds the tube
reaches its highest mechanical alloys. After a complete cycle of heat
treatments, the result is a extremely resistant matter, so it is possible
to lighten the tubes although they have to suffer welding processes to
be a part of a frame.

A Frame is Not a BikeOf course, we needed something more than three frames to take
conclusions. Such special structures deserve special components. Two of
the bikes had nice and special components: The Cannondale came from the
factory with some pieces that you will not find on another bike from another
brand, and the KHS was bought as a frame and later assembled with components
that are not very common. What about the third one? A Manitou SX-R and an
almost complete Deore XT set is not a bad thing, but all these components
come from an old M2 frame, so they are a little worn, and maybe this frame
deserves new and nicest pieces (except for the excellent fork as we will
say later). Its owner also thinks so and he is trying to save some bucks
(Euros here) to improve the machine.